1. Field of Invention
The present invention relates to a coating composition for simultaneously chromating a metallic surface and forming an organic resin coating on the metallic surface. More particularly, the present invention relates to a coating composition for metal, which enables the formation of a coating having improved lubricating property.
The general application of the coating composition for metal according to the present invention is for production of surface-treated metallic materials, to which lubricating property, formability, corrosion-resistance, paint adhesion, post-painting corrosion-resistance, and resistance against finger marks are imparted. In the coating-formation process, metallic materials, such as steel, aluminum, zinc, tin, copper, and their alloys in the form of coils, sheets, wires, or rods are subjected to the formation of a coating on the surfaces thereof.
2. Description of Related Arts
Heretofore in the field of metal-forming and painting on metals, the above described metallic materials have been generally subjected, subsequent to forming thereof or prior to paint-coating thereon, to such surface treatment as chromating or phosphating. Recently, in order to omit the coating step in the forming or paint-coating process thereby reducing cost, an attempt has been made for the above described metallic materials to be preliminarily surface-treated to form a coating and then subjected to application of press oil, followed by forming. The preliminarily surface-treated metallic materials may be degreased and then subjected to paint coating; that is, surface treatment steps, such as chromating and phosphating, are omitted during the production process of the final products. The metallic materials are, therefore, formed and/or paint-coated, but are neither chromated nor phosphatized in the production step of the final product. Several articles are already actually produced by this method.
Application of an aqueous resin and chromating agent is one of the representative methods for coating metallic materials. In one method for such application, reaction-type chromating agents are applied, followed by water rinsing, and then an agent mainly composed of organic resin is applied. According to another, aqueous resin, in which chromating agents are blended (hereinafter referred to as the "chromate-containing aqueous resin") is applied. The former method is disclosed, for example, in Japanese Unexamined Patent Publication No. 58-224,175, while the latter method is disclosed, for example, in Japanese Unexamined Patent Publication No. 63-145,785. According to these methods, labor can be saved and cost can be reduced because the chromating of final products can be omitted. The present applicant is one of the co-applicants of the Japanese Unexamined Patent Publication No. 63-145,785. The surface-treated materials produced by this method exhibit improved resistance against corrosion and finger marks. These properties are not degraded after alkali degreasing or solvent degreasing. These methods are, therefore, used widely, particularly by makers of home electric appliances.
When the surface-treated material, which is produced by the above described methods, is formed, it exhibits improved formability over the conventionally surface-treated steel, i.e., phosphated or chromated steel, because the resin layer applied by the above described methods is present, as an intermediary, between the metallic material and the tool. The formability is, however unsatisfactory, in that the surface-treated material must preliminarily be subjected to application of press oil or the like and then be formed. The preliminary application of press oil or the like is necessary regardless of the kind of coating, that is, the reaction type chromating followed by resin coating or the coating of the chromate-containing aqueous resin. The once applied oil or the like must be removed in the degreasing step prior to the paint-coating step. The degreasing and subsequent paint-coating steps are, however, complicated.